1. Field
Certain aspects of the present disclosure generally relate to wireless communication and, more particularly, to a method for sending control information to multiple user terminals that share the same resource.
2. Background
In order to address the issue of increasing bandwidth requirements demanded for wireless communication systems, different schemes are being developed to allow multiple user terminals to communicate with a single access point by sharing the same channel (same time and frequency resources) while achieving high data throughputs. Spatial Division Multiple Access (SDMA) represents one such approach that has recently emerged as a popular technique for the next generation communication systems. SDMA techniques are adopted in several emerging wireless communications standards such as Institute of Electrical and Electronic Engineers (IEEE) 802.11 and Long Term Evolution (LTE).
In SDMA systems, an access point can transmit or receive different signals to or from a plurality of user terminals at the same time and using the same bandwidth. In order to achieve reliable data communications, signals dedicated to different user terminals need to be located in sufficiently different directions. Independent signals may be simultaneously transmitted from each of multiple space-separated antennas located at the access point. Consequently, the combined transmissions are mutually directional; i.e., the signal that is dedicated for each user terminal is relatively strong in the direction of that particular user terminal, and sufficiently weak in directions of other user terminals. Similarly, the access point simultaneously receives on the same frequency the combined signals from multiple user terminals through each of multiple antennas separated in space, and the combined received signals from the multiple antennas can be split into independent signals transmitted from each user terminal by applying the appropriate signal processing techniques.
A multi-antenna communication system employs multiple transmit antennas at a transmitting entity and one or more receive antennas at a receiving entity for data transmission. The multi-antenna communication system can thus be a multiple-input multiple-output (MIMO) system. The MIMO system employs multiple (Nt) transmit antennas and multiple (Nr) receive antennas for data transmission. In a multiple-access MIMO system based on the SDMA technique, an access point can communicate with one or more user terminals at any given moment. If the access point communicates with a single user terminal, then the Nt transmit antennas are associated with one transmitting entity (either the access point or the user terminal), and the Nr receive antennas are associated with one receiving entity (either the user terminal or the access point). The access point can also simultaneously communicate with multiple user terminals via SDMA. In general, for SDMA, the access point utilizes multiple antennas for data transmission and reception, and each of the user terminals typically utilize less than the number of access point antennas for data transmission and reception.
In the SDMA wireless system, the access point can send traffic data and control information on the downlink to a user terminal. The control information is typically sent on control channels and may convey a downlink assignment, an uplink assignment, and/or other useful information for the user terminal. For example, the information conveyed by a physical downlink control channel (PDCCH) can include: a resource blocks (RB) assignment, a transmit power control (TPC) command for a physical uplink control channel (PUCCH), a hybrid automatic repeat-request (HARQ) process number, a HARQ swap flag, precoding information, precoding confirmation, modulation and coding scheme, a new data indicator, and a redundancy version.
In the current Evolved UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access (E-UTRA) specification, six different downlink control information formats can be defined: format 0 dedicated for Uplink Shared Channel (UL-SCH) assignments, format 1 dedicated for Downlink Shared Channel (DL-SCH) assignments for single-input multiple-output (SIMO) systems, format 1A representing a compact DL-SCH format, format 2 dedicated for DL-SCH assignments for MIMO systems, format 3 dedicated for group Transmit Power Control (TPC) with 2-bit adjustments, and format 3A dedicated for group TPC with single-bit adjustments.
For both uplink and downlink operations of the SDMA system, a number of required physical downlink control channels (PDCCHs) equals to a number of user terminals that share the same resources. Since the resource allocations for user terminals in the SDMA system are identical, certain benefits may be achieved if all user terminals that share same resources employ only one PDCCH. The reduced number of required PDCCH further decreases the overall PDCCH overhead in the SDMA system.